2,591 research outputs found
Marginalising instrument systematics in HST WFC3 transit lightcurves
Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) infrared observations
at 1.1-1.7m probe primarily the HO absorption band at 1.4m, and
has provided low resolution transmission spectra for a wide range of
exoplanets. We present the application of marginalisation based on Gibson
(2014) to analyse exoplanet transit lightcurves obtained from HST WFC3, to
better determine important transit parameters such as R/R, important
for accurate detections of HO. We approximate the evidence, often referred
to as the marginal likelihood, for a grid of systematic models using the Akaike
Information Criterion (AIC). We then calculate the evidence-based weight
assigned to each systematic model and use the information from all tested
models to calculate the final marginalised transit parameters for both the
band-integrated, and spectroscopic lightcurves to construct the transmission
spectrum. We find that a majority of the highest weight models contain a
correction for a linear trend in time, as well as corrections related to HST
orbital phase. We additionally test the dependence on the shift in spectral
wavelength position over the course of the observations and find that
spectroscopic wavelength shifts , best describe the
associated systematic in the spectroscopic lightcurves for most targets, while
fast scan rate observations of bright targets require an additional level of
processing to produce a robust transmission spectrum. The use of
marginalisation allows for transparent interpretation and understanding of the
instrument and the impact of each systematic evaluated statistically for each
dataset, expanding the ability to make true and comprehensive comparisons
between exoplanet atmospheres.Comment: 19 pages, 13 figures, 8 tables, Accepted to Ap
Corrigendum to "The upper atmosphere of the exoplanet HD209458b revealed by the sodium D lines: Temperature-pressure profile, ionization layer and thermosphere" [2011, A&A, 527, A110]
An error was detected in the code used for the analysis of the HD209458b
sodium profile (Vidal-Madjar et al. 2011). Here we present an updated T-P
profile and briefly discuss the consequences.Comment: Published in Astronomy & Astrophysics, 533, C
Perioperative thromboprophylaxis in digital replantation: a systematic review
Background There is no international consensus on the use of perioperative thromboprophylaxis in digital replantation. Suboptimal perioperative management may lead to replant failure which compromises extremity function, worsens psychosocial outcomes for patients and incurs significant cost. This systematic review evaluates and compares the efficacy and safety of perioperative antithrombotic protocols used in digital replantation. Methods A PRISMA-compliant prospectively registered (PROSPERO CRD42018108695) systematic review was conducted. Cochrane Central Register of Controlled Trials, Medline, EMBASE and Scopus were searched up until December 2019. Articles were assessed for eligibility in duplicate by two independent reviewers. All comparative studies which examined the use of perioperative thromboprophylaxis in digital replantation were eligible for inclusion. Results Collectively, 1,025 studies were identified of which 7 met full inclusion criteria reporting data from 635 patients (908 digital replants, 86% male, average age 37.3 years). Laceration was the most commonly reported mechanism of injury (68%) with 33% of replantation occurring in Tamai zone III. Fourteen distinct perioperative protocols were identified. One study reported significantly higher digital survival with continuous heparin infusion versus bolus heparin. Five studies demonstrated a significantly higher incidence of complications amongst patients treated with systemic heparin. Conclusions The clinical efficacy and safety of peri-operative antithrombotic therapy following digital replantation remains equivocal. The perceived benefits of improved digital survival must be tempered against the adverse systemic side effects of antithrombotic and anticoagulant therapies until further prospectively collected data sets become available
On the interaction between corrosion and fatigue which determines the remaining life of bridges
This paper studies the combined effect of corrosion and fatigue on the growth of cracks that arise from natural corrosion in steel bridges. It is shown that if these two effects need to be simultaneously analysed. If not then the resulting life is not conservative. Consequently, to enable a better understanding of the remaining life of steel bridges this paper presents a simple methodology for performing this coupled analysis
Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide
We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C}
270K and ferromagnetic to canted spin glass state at T_f\leq$ 125K is
observed
Transit spectrophotometry of the exoplanet HD189733b. II. New Spitzer observations at 3.6 microns
We present a new primary transit observation of the hot-jupiter HD189733b,
obtained at 3.6 microns with the Infrared Array Camera (IRAC) onboard the
Spitzer Space Telescope. Previous measurements at 3.6 microns suffered from
strong systematics and conclusions could hardly be obtained with confidence on
the water detection by comparison of the 3.6 and 5.8 microns observations. We
use a high S/N Spitzer photometric transit light curve to improve the precision
of the near infrared radius of the planet at 3.6 microns. The observation has
been performed using high-cadence time series integrated in the subarray mode.
We are able to derive accurate system parameters, including planet-to-star
radius ratio, impact parameter, scale of the system, and central time of the
transit from the fits of the transit light curve. We compare the results with
transmission spectroscopic models and with results from previous observations
at the same wavelength. We obtained the following system parameters:
R_p/R_\star=0.15566+0.00011-0.00024, b=0.661+0.0053-0.0050, and
a/R_\star=8.925+0.0490-0.0523 at 3.6 microns. These measurements are three
times more accurate than previous studies at this wavelength because they
benefit from greater observational efficiency and less statistic and systematic
errors. Nonetheless, we find that the radius ratio has to be corrected for
stellar activity and present a method to do so using ground-based long-duration
photometric follow-up in the V-band. The resulting planet-to-star radius ratio
corrected for the stellar variability is in agreement with the previous
measurement obtained in the same bandpass (Desert et al. 2009). We also discuss
that water vapour could not be evidenced by comparison of the planetary radius
measured at 3.6 and 5.8 microns, because the radius measured at 3.6 microns is
affected by absorption by other species, possibly Rayleigh scattering by haze.Comment: 19 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Hubble Space Telescope Transmission Spectroscopy of the Exoplanet HD 189733b: High-altitude atmospheric haze in the optical and near-UV with STIS
We present Hubble Space Telescope optical and near-ultraviolet transmission
spectra of the transiting hot-Jupiter HD189733b, taken with the repaired Space
Telescope Imaging Spectrograph (STIS) instrument. The resulting spectra cover
the range 2900-5700 Ang and reach per-exposure signal-to-noise levels greater
than 11,000 within a 500 Ang bandwidth. We used time series spectra obtained
during two transit events to determine the wavelength dependance of the
planetary radius and measure the exoplanet's atmospheric transmission spectrum
for the first time over this wavelength range. Our measurements, in conjunction
with existing HST spectra, now provide a broadband transmission spectrum
covering the full optical regime. The STIS data also shows unambiguous evidence
of a large occulted stellar spot during one of our transit events, which we use
to place constraints on the characteristics of the K dwarf's stellar spots,
estimating spot temperatures around Teff~4250 K. With contemporaneous
ground-based photometric monitoring of the stellar variability, we also measure
the correlation between the stellar activity level and transit-measured
planet-to-star radius contrast, which is in good agreement with predictions. We
find a planetary transmission spectrum in good agreement with that of Rayleigh
scattering from a high-altitude atmospheric haze as previously found from HST
ACS camera. The high-altitude haze is now found to cover the entire optical
regime and is well characterised by Rayleigh scattering. These findings suggest
that haze may be a globally dominant atmospheric feature of the planet which
would result in a high optical albedo at shorter optical wavelengths.Comment: 14 pages, 14 figures, 4 tables, accepted to MNRAS, revised version
has minor change
High-energy photoemission on Fe3O4: Small polaron physics and the Verwey transition
We have studied the electronic structure and charge ordering (Verwey)
transition of magnetite (Fe3O4) by soft x-ray photoemission. Due to the
enhanced probing depth and the use of different surface preparations we are
able to distinguish surface and volume effects in the spectra. The pseudogap
behavior of the intrinsic spectra and its temperature dependence give evidence
for the existence of strongly bound small polarons consistent with both dc and
optical conductivity. Together with other recent structural and theoretical
results our findings support a picture in which the Verwey transition contains
elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb
interaction
Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy
The optical properties of magnetite at room temperature were studied by
infrared reflectivity measurements as a function of pressure up to 8 GPa. The
optical conductivity spectrum consists of a Drude term, two sharp phonon modes,
a far-infrared band at around 600 cm, and a pronounced mid-infrared
absorption band. With increasing pressure both absorption bands shift to lower
frequencies and the phonon modes harden in a linear fashion. Based on the shape
of the MIR band, the temperature dependence of the dc transport data, and the
occurrence of the far-infrared band in the optical conductivity spectrum the
polaronic coupling strength in magnetite at room temperature should be
classified as intermediate. For the lower-energy phonon mode an abrupt increase
of the linear pressure coefficient occurs at around 6 GPa, which could be
attributed to minor alterations of the charge distribution among the different
Fe sites.Comment: 7 pages, 7 figure
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